Thermal sludge to energy transformer

Abstract

Systems and processes provide for a thermal process to transform sludge (and a variety of other natural waste materials) into electricity. Dewatered sludge and other materials containing a high amount of latent energy are dried into a powdered biofuel using a drying gas produced in the system. The drying gas is recirculated and is heated by the biofuel produced in the system, waste heat (from turbines or internal combustion engines), gas (including natural gas or digester gas) and/or oil. The biofuel is combusted in a boiler system that utilizes a burner operable to burn biofuel and produce heat utilized in a series of heat exchangers that heat the recirculating drying air and steam that powers the turbines for electricity production.

What is claimed is: 
     
         1 . A system for generating electricity by combusting biofuel produced from dewatered sludge, the system comprising:
 a dryer operable to:
 receive a drying gas; 
 receive sludge; and 
 reduce the moisture content of the sludge in the presence of the drying gas, wherein the drying gas absorbs at least a portion of the moisture content of the sludge and forms a biofuel, reduced moisture powder, and at least partially saturated gas; 
   a boiler system operable to combust the biofuel to produce at least one of heat for use in the dryer or steam for a turbine;   a first separator operable to separate the biofuel from the at least partially saturated gas;   a first condenser operable to reduce a moisture content of the at least partially saturated gas by reducing a temperature of the at least partially saturated gas to form a reduced-moisture gas;   at least one fan operable to direct the reduced-moisture gas to the heat exchanger to form the drying gas, the heat exchanger disposed in the boiler system and to direct the reduced-moister gas to the dryer to reduce the moisture content of the sludge;   a diverter valve operable to keep an overall system moisture balance by removing the volume of reduced-moisture gas out of the system that is equivalent to the volume of moisture removed from the sludge less the amount removed by first condenser;   a make-up air supply to replace reduced-moisture gas diverted out of the system;   a series of heat exchangers incorporated into the boiler system to transfer heat to at least one of the turbine and dryer.   
     
     
         2 . The system of  claim 1 , wherein the sludge comprises at least one or a combination of digested sludge, undigested sludge, fresh animal waste, aged animal waste, agricultural waste, or food waste. 
     
     
         3 . The system of  claim 1 , further comprising a mixer operable to mix a second portion of reduced-moisture gas with gas heated by the boiler to form the drying gas. 
     
     
         4 . The system of  claim 3 , wherein the boiler system comprises a burner operable to burn a mixture of at least one of ambient and pre-heated air and at least a portion of the dried powder. 
     
     
         5 . The system of  claim 3 , wherein the burner is further operable to burn a gas or oil. 
     
     
         6 . The system of  claim 1 , further comprising a heater having a gas burner, the heater operable to further heat the drying gas heated by the boiler system. 
     
     
         7 . The system of  claim 1 , wherein the reduced-moisture gas is preheated using heat from combusted gas before it is heated in the boiler system 
     
     
         8 . A method for producing electricity from dewatered sludge in a treatment system, the method comprising:
 reducing moisture content of a dewatered sludge in a dryer by breaking the dewatered sludge into biofuel in the presence of a drying gas, wherein the drying gas absorbs at least a portion of the moisture content of the dewatered sludge to form at least partially saturated gas;   combusting the biofuel to produce at least one of a drying gas for use in the drying process and steam for use in a turbine;   separating the biofuel from the at least partially saturated gas;   reducing a moisture content of the at least partially saturated gas by reducing a temperature of the at least partially saturated gas to below its dew point in order to form a reduced-moisture gas;   heating a portion of the reduced-moisture gas to generate the drying gas; and   recirculating at least a portion of the drying gas by directing it to the dryer, wherein upon exiting the dryer it becomes partially saturated gas.   
     
     
         9 . The method of  claim 8 , wherein the steam exiting the turbine is preheated using heat from power generation equipment exhaust prior to being heated in the boiler system. 
     
     
         10 . The method of  claim 8 , wherein a duel fuel burner of a boiler system is used to combust the fuel and the boiler system heats the drying gas. 
     
     
         11 . The method of  claim 10 , wherein the drying gas is heated by a heater burning gas and the system boiler. 
     
     
         12 . The method of  claim 10 , wherein the drying gas is heated by power generation equipment exhaust gas and the system boiler. 
     
     
         13 . The method of  claim 10 , wherein, the fuel includes a mixture comprising biofuel, ambient air, and heated process air. 
     
     
         14 . The method of  claim 9 , wherein the drying gas is heated by at least one of a heater burning gas, power generation equipment exhaust gas, and a system boiler. 
     
     
         15 . The method of  claim 8 , wherein reducing the moisture content of the at least partially saturated gas is performed using a condenser operable to receive water at a first temperature and output the water at a second temperature higher than the first temperature, and wherein the water reduces the temperature of the at least partially saturated gas. 
     
     
         16 . The method of  claim 8 , wherein combusting the fuel produces combusted gas having ash and a moisture content, and further comprising:
 reducing the moisture content of the combusted gas using a condenser, the condenser operable to receive water at a first temperature and output the water at a second temperature higher than the first temperature, and wherein the water reduces the temperature of the combusted gas;   discharging the reduced moisture combusted gas; and   separating the ash from the combusted gas.   
     
     
         17 . A system for generating electricity by using fuel produced from processing dewatered sludge into a biofuel, the system comprising:
 a dryer operable to:
 receive a drying gas; 
 receive sludge; and 
 reduce the moisture content of the sludge in the presence of the drying gas, thereby forming a biofuel comprising dried powder and an at least partially saturated gas; wherein the drying gas breaks down the sludge and absorbs at least a portion of the moisture content of the sludge to form into a biofuel, the biofuel comprising dried powder, and an at least partially saturated gas; 
   a boiler operable to combust the biofuel; and   a condenser operable to reduce a moisture content of the at least partially saturated gas by reducing a temperature of the at least partially saturated gas to form a reduced-moisture gas; and   a diverter operable to vent a volume of reduced-moisture gas based on a volume of moisture contained in the sludge introduced into the system.   
     
     
         18 . The system of  claim 17 , further comprising a series of heat exchangers incorporated into the boiler system to transfer heat to at least one of a turbine and the dryer. 
     
     
         19 . A method for producing electricity from dewatered sludge in a treatment system, the method comprising:
 reducing moisture content of a dewatered sludge by breaking the dewatered sludge into biofuel in the presence of a drying gas, wherein the drying gas absorbs at least a portion of the moisture content of the dewatered sludge to form at least partially saturated gas;   separating the biofuel from the at least partially saturated gas;   combusting the biofuel to produce at least one of a drying gas for use in the drying process and steam for use in a turbine;   
     
     
         20 . The method of  claim 19 , further comprising:
 reducing a moisture content of the at least partially saturated gas by reducing a temperature of the at least partially saturated gas to below its dew point in order to form a reduced-moisture gas; and   heating a portion of the reduced-moisture gas to generate the drying gas; recirculating at least a portion of the drying gas by directing it to the dryer, wherein upon exiting the dryer it becomes partially saturated gas.